Hitherto, SnapOPC (Snapshot One Point Copy) has been known as one of methods for backing up data in a storage apparatus. SnapOPC is a method that creates the backup of only an updated part of the data in a copy source volume in creating the backup data.
Furthermore, in recent years, as an extension function of SnapOPC, a method called SnapOPC+ that creates backup data for each generation has been proposed. More specifically, SnapOPC+ creates a Snap Data Volume (which will be called SDV hereinafter) which is a backup volume for each generation (such as for each day of the week) and copies the differential data between generations to the SDV.
For example, as illustrated in FIG. 19, a storage apparatus implementing SnapOPC+ creates Monday SDV 2a, Tuesday SDV 2b and Wednesday SDV 2c on Monday, Tuesday and Wednesday as backup volumes of a copy source volume 1. At that time, the Monday SDV 2a only stores the updated part of the data from Monday, and the Tuesday SDV 2b only stores the updated part of the data from Tuesday. The Wednesday SDV 2c only stores the updated part of the data from Wednesday.
By the way, in such a storage apparatus, in order to restore the current state of a copy source volume to a state of an arbitrary generation, a host apparatus 3, which connects to the storage apparatus 25, first instructs to execute the restoration, as illustrated in FIG. 20. Here, it is assumed that the instruction has been given for restoring the current state of the copy source to the Tuesday's state.
The storage apparatus 25 in response to the restore execution instruction recovers as the state of the data of Tuesday on the basis of the data (current data) stored in the copy source volume 1 and the differential data stored in the Tuesday SDV 2b and Wednesday SDV 2c. Then, the host apparatus 3 reads out the recovered data and updates the source volume with the read data. Thus, the current state of the copy source can be restored to the data as of Tuesday (refer to Japanese Laid-open Patent Publication No. 2006-107162, for example).
However, as illustrated in FIG. 20, the host apparatus 3 only recognizes that all data of a generation is stored in the corresponding backup volume of the generation, unlike its actual volume size. Therefore, when restoration is executed through the host apparatus 3, the processing of rewriting an updated part only is difficult to perform, and the data in the copy source is entirely rewritten as described above. This means that the part which has not been updated is also rewritten, which may possibly take unnecessary time for the restoration. Furthermore, the data reading processing and writing processing may task the host apparatus.